The invention pertains to the field of pumps for liquid chromatography systems, and, more specifically, to the field of systems to insure proper check valve closure for same.
In the prior art, check valve closure for injection pumps for liquid chromatography systems was checked by timing the time it takes the pump to move through the segment of a revolution where the valve was closing. Because such systems have control loops that control the motor speed in response to both pressure on the column input and desired flow rate with two separate control loops, each responsive to one of these criteria, such systems were not reliable. The reason for this was that the time taken by the pump to move through the segment of the revolution where the check valve was supposed to be closing varied by the action of the control loops in changing the motor speed. A more reliable indication of failure of the check valve was necessary.